hasPrefix misbehave on Optional String

Question

Why does the following always print "prefix" which is incorrect but print "no prefix" when String is not optional or implicitly unwrapped optional?

var value:String! = "aaa"  // Same incorrect behavior on Optional String as well.
if value?.hasPrefix("bbb") {
    NSLog("prefix")
}
else {
    NSLog("no prefix")
}

Answer 1

The if statement is checking if the statement returns a value or nil, not if it returns true or false. You can use another if statement to check the value of hasPrefix().

var value:String! = "aaa"  // Same incorrect behavior on Optional String as well.
if let hasPrefix = value?.hasPrefix("bbb") {
    if hasPrefix{
        NSLog("prefix")
    }
    else {
        NSLog("no prefix")
    }
}
else {
    NSLog("nil value")
}